HEJA stands for High-Explosive Jet-Assisted. “HEJA rounds are unique in that they increase in speed once they leave the muzzle due to the gyrojet engine that ignites seconds after clearing the cannon. Utilizing a fast-burning solid propellant, HEJA rounds are designed to destroy fast-moving or long-range opponents. They have a maximum effective distance comparable to military anti-aircraft guns.”*
Does this type of ammunition actually exist outside of science fiction? My Google searches didn’t turn up anything, but I wanted to see if anyone knew if it was an existing technology.
Well, a quick ‘Google’ failed to turn-up any substantiated sites, save for fiction. OTOH, RAP (Rocket-Assisted Projectiles) and Base-Bleed shells have been around for some years, and Gyro-Jet Pistols were actually issued in Viet Nam. Talley Defense Systems has HERA (High-Explosive Rocket-Assisted) projectiles.
The ERGM from this site is a Guided RAP.
So, sorry, no HEJA, but there’s plenty of other cool ordnace that comes close.
Thanks for your help, Tranquilis. That Gyro-Jet Pistol is close to what I’m looking for. Um, not literally, I mean. I’m writing a book that takes place in the future, and I wanted to make sure this wasn’t already perfected technology.
As a nitpick that might clear this up a little, the round you’re describing is a rocket, not a jet. Solid propellants tend to clog the pumps and turbines in most jets. “Gyrojet” is also a brand name for a spin-stabilized, pistol-launched rocket, not a technical classification.
In fact, it seems Tranquilis has found exactly what you’re looking for in RAP, though they seem to be indirect-fire rounds rather than high-velocity direct-fire weapons.
From what I’ve read, these rocket assisted bullet type systems generally don’t work too well. Once you are outside the barrel, the rocket igniting could send the projectile somewhat off course. I’ve heard the aforementioned MBA gyrojet pistols used in Vietnam, for example, were virtually useless in any kind of a breeze and that accuracy dropped substantially with any kind of distance.
My book is about a weapons research facility that has plans for HEJA rounds stolen by an employee. My heroine’s job is to return the plans and capture the bad guy. It takes place in 2053, so I needed to be sure that HEJA didn’t actually exist so this research facility could invent it.
No solid evidence, but someone who knows this sort of thing once sketched me a rather simple propellant-assisted round ten or more years ago, for what type of gun, I do not know. It was supposedly being constructed at Radford Arsenal, in southern Virginia.
Basically, it was an artillery round–or perhaps a bullet–with a hole in the back end and a second chamber in the rear of the round that contained a propellant which was ignited when the main charge fired. I think it was actually designed to fully ignite outside of the barrel, but I’m not sure of that. Presumably the barrel was rifled so that spin was already imparted on the projectile.
I guess it could have simply been a tracer round, but I got the impression that the simple rocket mechanism was designed to accelerate the projectile to armor-piercing velocities.
The Swedish-made 84 mm recoilless rifle (Carl Gustav) uses a rocket engine to increase range in some of the anti-armour rounds. The rounds are fin-stabilized and do not spin (spinning reduces the efficiency of shaped-charge warheads, anyway).
It works quite well, except that you need a team of mathematicians to correct for windage: “The target is 350 m away, wind is 8 m/s from the right, rocket engine kicks in after 120 m. I’ll have to correct to the right for 120 m free flight, then to the left for 230 m of rocket-assisted flight where the the wind pressure on the fins will make the projectile veer into the wind, resulting in, lessee, - Oh, the target got bored and left.” (OK, in practice, the gunner memorizes quite a table of corrections for different windspeeds and distances. It’s a difficult weapon to use.)
The problem with rocket-assisting traditional spin-stabilized ordnance is that any jitter and toppling in the trajectory is increased by the rocket engine - so while you might get some extra range, you pay for it with decreased accuracy. Doubling the inaccuracy means expending four to eight times the amount of ordnance for the same effect. Not a happy prospect for the logistics staff.
Rotating projectiles such as the Gyro-Jet tend to compensate for this by constantly increasing the rate of rotation of the round. As the rocket fuel burns, the round becomes lighter, and the rate of change of rotation actually increases slightly. The increased angular velocity tends to counter stability issues caused the decreasing weight of the projectile and evens-out minor differences in thrust between nozzles. In general, lighter rounds need to rotate faster to remain stable. Careful selection of nozzle angle, shape, and rate of burn will keep a gyro round stable. Also, as the grain burns, the center of gravity changes slightly, which also has an effect on inflight behavior of the round. There are a number of interesting and inter-related forces at work on a bullet or artillery shell, beyond the scope of the OP. Simplistically put, the nose of a well-designed projectile describes a circle around the axis of the direction of flight for most of it’s flight. More than you ever wanted to know on the subject.
The kinds of calculations, research and design effort necessary to solve accuracy and stability issues while increasing range and/or velocity would be a prime target for industrial espionage, as stealing them would tremendously reduce development time and costs, and would be virtually untraceable in the final product.
As for the Gyro-Jet pistol, reports of it’s inaccuracy are greatly exagerated. Here, from someone who actually carried one in Viet Nam:
As for the power and penetration of it, well, this says it all:
We played with RAP’s and Gyro-Jet’s a bit in China Lake and they were generally not worth the trouble. Neat concept but even with near perfect design, a production nightmare and rather costly. Not enough bang for the buck compared to standard rounds.
There is a 4 inch projectile that is basically a scaled down missile, that uses a scramjet that is being worked on now to eventually scale up to develop the missile. Not exactly a gun, but it might give you an idea of current technologies and possibilities. From a publication:
These items show up in the James Bond movie You Only Live Twice – both jet-assisted “bullets” and little spy-type projectiles hidden in cigarettes (“It can save your life, this cigarette!” says “Tiger” Tanaka. “You sound like a commercial,” comments Bond.)(It’s only in the movie – there’s nothing like it in Fleming’s book.) I recall that somewhere in discussions about this item someone pointed out that the projectiles were only good for short range, since they were so inaccurate. Judging from the above entries, they’re not even that accurate over short ranges.
Gerald Bull worked on the reverse of this concept. He designed small rockets to be boosted by large guns, as well as bleeder systems to make artillery rounds fly further. I can’t explain it much better than that- check out this page http://world.std.com/~jlr/doom/bull.htm
I also heard that this is being used for rounds that adjust themselves in midflight, which makes their point of origin difficult for anti-artilelry to pick up.
Currently, the most widely used range extention technologies are:
Base Bleed
Air Delivery
Base Bleed puts a rocket-like grain at the base of the projectile, but one that burns fairly slowly. Rather than “propel” the shell, the gasses from the grain merely fills the void created behind the shell as it flies through tha air, greatly reducing drag by eliminating the low-pressure zone.